Question
Given two integers dividend
and divisor
, divide two integers without using multiplication, division and mod operator.
Return the quotient after dividing dividend
by divisor
.
The integer division should truncate toward zero.
Example 1:
Input: dividend = 10, divisor = 3 Output: 3
Example 2:
Input: dividend = 7, divisor = -3 Output: -2
Note:
- Both dividend and divisor will be 32-bit signed integers.
- The divisor will never be 0.
- Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 231 − 1 when the division result overflows.
Difficulty:Medium
Category:
Solution
这道题目规定我们不能使用乘法,除法以及取余操作。我们可以考虑在这道题目使用 Bit Operation
以下分析来自于博文:Divide Two Integers 两数相除 这道题让我们求两数相除,而且规定我们不能用乘法,除法和取余操作,那么我们还可以用另一神器位操作Bit Operation,思路是,如果被除数大于或等于除数,则进行如下循环,定义变量t等于除数,定义计数p,当t的两倍小于等于被除数时,进行如下循环,t扩大一倍,p扩大一倍,然后更新res和m。这道题的OJ给的一些test case非常的讨厌,因为输入的都是int型,比如被除数是-2147483648,在int范围内,当除数是-1时,结果就超出了int范围,需要返回INT_MAX,所以对于这种情况我们就在开始用if判定,将其和除数为0的情况放一起判定,返回INT_MAX。然后我们还要根据被除数和除数的正负来确定返回值的正负,这里我们采用长整型long来完成所有的计算,最后返回值乘以符号即可
Solution 1: Implement
class Solution {
public:
int divide(int dividend, int divisor) {
long long m = abs((long long)dividend), n = abs((long long)divisor), res = 0;
if (m < n) return 0;
while (m >= n) {
long long t = n, p = 1;
while (m > (t << 1)) {
t <<= 1;
p <<= 1;
}
res += p;
m -= t;
}
if ((dividend < 0) ^ (divisor < 0)) res = -res;
return res > INT_MAX ? INT_MAX : res;
}
};
Solution 2: Recursion
class Solution {
public:
int divide(int dividend, int divisor) {
long long res = 0;
long long m = abs((long long)dividend), n = abs((long long)divisor);
if (m < n) return 0;
long long t = n, p = 1;
while (m > (t << 1)) {
t <<= 1;
p <<= 1;
}
res += p + divide(m - t, n);
if ((dividend < 0) ^ (divisor < 0)) res = -res;
return res > INT_MAX ? INT_MAX : res;
}
};